Non-aqueous electrolyte comprising an aluminum compound, cells using the electrolyte and a method for the electrodeposition of aluminum from the electrolyte

ABSTRACT

A non-aqueous electrolyte comprises an aluminum halide and a quaternary ammonium halide dissolved in a non-aqueous solvent. A non-aqueous electrolytic cell is also described, which comprises an anode made od Al or its alloy, an cathode and the non-aqueous electrolyte provided between the anode and the cathode. The non-aqueous electrolyte is suitable for electrodeposition of aluminum from the electrolyte. Because aluminum is reversibly electrodeposited from and dissolved in the electrolyte, the electrolyte is usable for making secondary cells having good charge and discharge characteristics and a high energy density.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims the benefit of theearlier filing dates of, U.S. application Ser. No. 08/103,792, filedAug. 10, 1993, now U.S. Pat. No. 6,083,647, which claims priority toJapanese patent applications JP P04-239041 (filed Aug. 14, 1992) and JPP05-045842 (filed Feb. 9, 1993); the disclosures of which are expresslyincorporated by reference to the extent permissible by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to non-aqueous electrolytes comprising aluminiumcompounds. The invention also relates to cells and an electrodepositionmethod using the non-aqueous electrolyte.

2. Description of the Related Art

It is considered that use of aluminium as an anode material of cellsleads to fabrication of cells with a high energy density at low costs.Accordingly, cells using an Al anode have been accepted as promising inthe future. This is because the theoretical energy density per unitvolume of Al is as high as 8050 Ah/l which is about four times largerthan that of lithium. In addition, the standard electrode potential ofan Al relative to a standard hydrogen electrode is −1.66 V, so that ifAl is used in combination with an appropriate cathode material, theresultant cell may be interchangeable with existing alkaline dry cellsor silver cells. In this sense, cells using Al as an anode are full ofpromise, for which developments of such cells have been extensivelymade. For this purpose, several problems have to be solved includingthose problems on the selection of liquid electrolyte, the selection ofelectrode material, and how to arrange a cell using an Al anode. Ofthese, it is the most important how to select or formulate electrolyte.

As is well known in the art, Al has been made according to an aluminaelectrolitic refining which requires a complicated operational procedureand a vast of electric power. Accordingly, there is a demand for theelectrodeposition of Al by a simple manner. In this case, the selectionof a liquid electrolyte is important.

In general, aluminium is more unlikely to be thermodynamically-reducedthan hydrogen, so that any electrochemical reversible reaction cannot beexpected in aqueous solution systems. In addition, aluminium has aninsulating and high-packed passive state natural oxide layer on thesurface due to high affinity for oxygen atoms. This makes it verydifficult to cause aluminium to be dissolved out at the time ofdischarge. As a consequence, polarity becomes great, or it will beassumed that the passive state layer is more grown through anodization.

Under these circumstances, electrolytes for primary or secondarybatteries or cells making use of Al or electrolytes used forelectrodeposition of Al have been proposed including, for example,organic solvent-based non-aqueous electrolytes such as used in lithiumelectrochemical cells, and ether-base or molten salt-based non-aqueouselectrolytes. In recent years, there has also been proposed use ofnon-aqueous electrolytes which comprise room temperature-molten saltscomposed of aluminium halides/N-alkylpyridinium halides, or roomtemperature-molten salts composed of aluminiumhalides/N-alkylimidazolinium halides.

In general, however, non-aqueous electrolytes have the problem thattheir conductivity are lower by one or two orders of magnitude than thatof aqueous electrolytes. For instance, where cells are fabricated usingorganic solvent-based non-aqueous electrolytes as used in lithiumelectrochemical cells, there arises the problem that because of the lowconductivity of the electrolyte, the load characteristics of theresultant cell are lowered. In addition to the problem on theconductivity, with the ether non-aqueous electrolytes, there is aproblem on handling because of the ease in firing of ethers. Withnon-aqueous electrolytes comprising molten salts, temperatures higherthan 200° C. are needed for working operations, thus presenting theproblem that it is not possible to work the cell at normal temperatures.With non-aqueous electrolytes comprising room temperature-molten salts,the workable range is so narrow that once the cell has been used outsidethe workable temperature range, the electrolyte may be solidified or thekind or concentration of ions in the electrolyte may be changed, with aserious problem on stability.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a non-aqueouselectrolyte which can solve the problems of the prior art counterparts.

It is another object of the invention to provide a non-aqueouselectrolyte which can reduce polarity on discharge of cells making useof an Al or Al alloy anode.

It is a further object of the invention to provide a non-aqueouselectrolyte which enables electrodeposition of Al at ambienttemperatures.

It is a still further object of the invention to provide a non-aqueouselectrolyte cell which makes use of the non-aqueous electrolytementioned above whereby good discharge characteristics are obtained.

It is another object of the invention to provide a method for theelectrodeposition of Al in which the electrolyte of the type mentionedabove is used.

In accordance with one embodiment of the invention, there is provided anon-aqueous electrolyte which comprises, in combination, an aluminiumhalide and a quaternary ammonium halide in a non-aqueous solvent.

When the non-aqueous electrolyte is applied to a cell which comprises ananode made of Al or an Al alloy, polarity at the time of discharge canbe reduced with good discharge characteristics.

According to another embodiment of the invention, there is also provideda non-aqueous electrolyte cell which comprises an anode made of Al or anAl alloy, a cathode in a spaced relation with the anode, and a separatorprovided between the anode and the cathode and impregnated with anon-aqueous electrolyte, the non-aqueous electrolyte comprising analuminium halide and a quaternary ammonium halide in a non-aqueoussolvent.

If the non-aqueous electrolyte of the invention is used, theelectrodeposition of Al can be conveniently conducted by a simplemanner.

Thus, according to a further embodiment of the invention, there isprovided a method for electrodepositing Al which comprises subjecting anon-aqueous electrolyte of the type set out above to electrodeposition.

When the non-aqueous electrolyte of the invention is used, Al can bereversibly electrodeposited from and dissolved in the non-aqueouselectrolyte. Accordingly, it will be possible to fabricate a secondarycell which exhibits good charge and discharge characteristics and has ahigh energy density.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relation between the concentration oftetraethylammonium chloride ((CH₃CH₂)₄N.Cl) in a non-aqueous electrolyteof the invention and the conductivity;

FIG. 2 is a graph showing the relation between the cell voltage and thedischarge time for a cell of the invention and a cell for comparison;

FIG. 3 is a graph similar to FIG. 2 but at a different dischargecurrent;

FIG. 4 is a graph showing the relation between the concentration ofdimethyl carbonate in a non-aqueous electrolyte of the invention and theconductivity;

FIG. 5 is a graph showing the relation between the cell voltage and thedischarge time at a constant current of 1 mA for a cell of the inventionand a cell for comparison; and

FIG. 6 is a schematic view of a cell according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The non-aqueous electrolyte of the invention should comprise, incombination, an aluminium halide and a quaternary ammonium halide in anon-aqueous solvent. The aluminium halides preferred in the presentinvention are anhydrous halides of the general formula, AlX₃, wherein Xrepresents Cl, Br or I. If the concentration of the aluminium halide istoo low, the capacitance of the resultant cell does not reach apractical level, resulting in too low conductivity. On the other hand,when the concentration is too high, the halide is unlikely to dissolvein a non-aqueous solvent. Preferably, the concentration is in the rangeof from 0.1 to 10.0 moles/liter of the electrolyte.

If the non-aqueous electrolyte is applied to a cell, the concentrationof the halide is more preferably in the range of 0.1 to 2.0 moles/literand most preferably from 0.75 to 1.5 moles/liter. On the other hand, ifthe electrolyte is applied for the electrodeposition, the concentrationof the halide is more preferably in the range of from 0.5 to 10.0moles/liter and most preferably from 1.3 to 3.3 moles/liter.

The quaternary ammonium halides which are the other ingredient of theelectrolyte of the invention are preferably those compounds of thefollowing formula

wherein R₁, R₂, R₃ and R₄ independently represent a hydrocarbon group,and Y is a counter ion. The hydrocarbon group has preferably up to 10carbon atoms. Examples of the hydrocarbon group include, an alkyl groupsuch as a methyl group, an ethyl group, a propyl group or the like, anaryl group such as a phenyl group, and an aralkyl group such as a benzylgroup. These hydrocarbon groups may have substituents such as atrifluoromethyl group. As a matter of course, R₁, R₂, R₃ and R₄ may bethe same or different. The counter ion represented by Y— may be variousanions such as a perchlorate ion, which are selected as required.Preferably, the counter ions include Cl⁻, Br⁻ and I⁻.

Specific examples of the quaternary ammonium halides includetetramethylammonium chloride, trimethylethylammonium chloride,trimethylphenylammonium chloride, trimethylbenzylammonium chloride,tetraethylammonium chloride, triethylmethylammonium chloride,triethylphenylammonium chloride and triethylbenzylammonium chloride.

The concentration of the quaternary ammonium halide is preferably in therange of from 0.01 to 2.0 moles/liter. The molar ratio of the quaternaryammonium halide to the aluminium halide is preferably in the range offrom 0.5 to 2:1. If the molar ratio is less than 0.5, part of thealuminium halide may not be dissolved in the electrolyte. If the molarratio is over 1, part of the quaternary ammonium halide may not bedissolved.

Where the non-aqueous electrolyte of the invention is used forelectrodeposition of Al, the electrodeposition favorably proceeds underconditions where the concentration of the aluminium halide is higherthan that of the quaternary ammonium halide. Accordingly, it ispreferred that the molar ratio of the quaternary ammonium halide to thealuminium halide is in the range of 0.5:1 to 1:1, more preferably from0.5:1 to 0.75:1.

The non-aqueous solvents for dissolution of both the quaternary ammoniumhalide and the aluminium halide may be compounds ordinarily used inknown lithium electrochemical cells. Examples of the solvent includepropylene carbonate, acetonitrile, γ-butyrolactone, tetrahydrofuran,2-methyl-tetrahydrofuran, dimethoxyethane, and mixtures thereof. In thiscase, these solvents should be subjected to dehydration to fully removethe moisture therefrom. In view of the solubility of anhydrous alkylquaternary ammonium halides, it is preferred to use propylene carbonateor a mixed solvent of propylene carbonate and dimethyl carbonate. If themixed solvent propylene carbonate and dimethyl carbonate is used, thecontent of dimethyl carbonate should preferably be up to 80% by volume.

Moreover, dehydrated acetonitrile or dehydrated organic solvents havinga donor number not larger than 5 are also preferably used as thenon-aqueous solvent of the invention. The term donor number is intendedto mean a degree of Lewis basicity of solvent which is defined byselecting 1×10⁻³ mol.dm⁻³ of antimony pentachloride in1,2-dichloroethane as a standard acceptor and determining an molarenthalpy value (kcal.mol⁻¹) for the reaction between the acceptor and adonor (solvent). A smaller value means in a lower basicity. Organicsolvents having a donor number of not larger than 5 include, forexample, 1,2-dichloroethane, 1,2-dichlorobenzene, 1,3-dichlorobenzene,and the like. These solvents having a donor number of not larger than 5are preferred especially when the non-aqueous electrolyte is used forthe electrodeposition of Al. This is for the following reason: theorganic solvent having a donor number of not larger than 5 is adaptedfor reversible dissolution of once electrodeposited aluminium.Accordingly, when an organic solvent having a donor number of not largerthan 5 is-used as a solvent of the non-aqueous electrolyte, theresultant electrolyte may be usable as a non-aqueous electrolyte forsecondary rechargeable cells.

Reference is now made to FIG. 6 which schematically shows a cell Caccording to the invention. The cell C includes a unit U which has ananode pellet 1, and a cathode 2 provided in a spaced relation with theanode pellet 1. A separator 3 is provided in the unit U between theanode 1 and the cathode 2. The cell unit U is accomodated in a resincasing 6. As a matter of course, current collectors 4, 5 may be,respectively, provided in contact with the anode 1 and the cathode 2.Leads 7, 8 are connected to the current collector 4, 5, respectively, asshown in the figure.

The cathode 1 should be made of Al or an Al alloy. Examples of the Alalloy include Al—Mg alloys having 97 to 99 atomic % of Al and,correspondingly, from 3 to 1 atomic % of Mg, and those alloys defined inJIS and including, for example, Al alloy Nos. 1100 (1.0 atomic % ofSi+Fe, 0.05 to 0.20 atomic % of Cu, 0.05 atomic % of Mn, 0.10 atomic %of Zn and the balance of Al, 3003 (0.6 atomic % of Si, 0.7 atomic % ofFe, 0.05 to 0.20 atomic % of Cu, 1.0 to 1.5 atomic % of Mn, 0.10 atomic% of Zn and the balance of Al, 5052 (0.3 atomic % of Si, 0.7 atomic % ofFe, 0.20 atomic % of Cu, 0,10 atomic % of Mn, 2.2 to 2.8 atomic % of Mg,0.10 atomic % of Cr, 0.25 atomic % of Zn and the balance of Al, and 6963(from 0.20 to 0.60 atomic % of Si, 0.35 atomic % of Fe, 0.10 atomic % ofCu, 0.10 atomic % of Mn, 0.45 to 0.90 atomic % of Mg, 0.10 atomic % ofCr, 0.10 atomic % of Zn, 0.10 atomic % of Ti and the balance of Al. Thecathode 2 may be made of compositions which are ordinarily used for thispurpose and comprise conductive agents and binder resins. A typicalcomposition comprises manganese dioxide, conductive agents such asgraphite, and resin binders such as fluorocarbon resins.

The non-aqueous electrolyte 3 is one which has been set out hereinabove.The casing 6 may be made of resins such as fluorocarbon resins and thelike.

Thus, the cell of the invention may be arranged by a usual manner exceptthat the anode consists of Al or its alloy and the non-aqueouselectrolyte is comprised of an aluminium halide and a quaternaryammonium halide.

Since the non-aqueous electrolyte of the invention comprises, in anon-aqueous solvent, an aluminium halide and a quaternary ammoniumhalide, the conductivity is pronouncedly improved. Accordingly, whenthis electrolyte is used to arrange a cell having an Al or Al alloyanode, breakage of the passive state oxide layer at the anode takesplace readily at the time of discharge. Eventually, the electrochemicalactivity at the anode are improved, with good discharge characteristics.

As stated above, the non-aqueous electrolyte of the invention comprisesan aluminium halide and a quaternary ammonium halide. Accordingly, it ispossible to electrodeposit Al from the electrolyte. Theelectrodeposition may be conducted by any known procedures under knownelectrodepositing conditions except that the non-aqueous electrolyte ofthe invention is used.

The invention is more particularly described by way of examples.

EXAMPLE 1

10 wt % of graphite as a conductive material and 5 wt % of afluorocarbon resin powder as a binder were added to 85 wt % ofelectrolytic manganese dioxide which had been annealed at apredetermined temperature, followed by mixing and shaping to obtain acathode.

Separately, a 100 μm thick aluminium sheet was provided as a cathode.

Anhydrous aluminium chloride (AlCl₃) was dissolved in dehydratedpropylene carbonate at a concentration of 1.0 mole/liter, followed bydissolution of anhydrous tetraethylammonium chloride thereby obtaining anon-aqueous electrolyte solution. In this connection, the amount oftetraethylammonium chloride being dissolved was changed to measureconductivity. The results are shown in FIG. 1, From the figure, it willbe seen that as the concentration of tetraethylammonium chlorideincreases, the conductivity also increases. The conductivity is beyond alevel which is necessary for practical applications.

A non-aqueous electrolyte wherein the concentration oftetraethylammonium chloride is 1.0 mole/liter or whose conductivity isthe highest among the non-aqueous electrolytes indicated in FIG. 1, wasused to fabricate a cell along with the anode and the cathode indicatedhereinbefore. The cell was subjected to measurement of dischargecharacteristics while discharging at constant currents of 0.1 mA and 0.3mA, respectively. The results are shown in FIGS. 2 and 3.

Comparative Example 1

The general procedure of Example 1 was repeated without use of anhydroustetramethylammonium chloride, thereby obtaining a non-aqueouselectrolyte and making a cell using the electrolyte. The cell wassubjected to measurement of discharge characteristics. The results areshown in FIGS. 2 and 3.

From the results of FIGS. 2 and 3, the cell of Example 1 has a greaterutilization efficiency of the anode than that of Comparative Example 1.Moreover, the load characteristic is also improved.

Comparative Example 2

The general procedure of Example 1 was repeated except that anhydrousaluminium chloride was not used, thereby obtaining a non-aqueouselectrolyte and making a cell. This cell was not worked as a cell.

EXAMPLE 2

Anhydrous aluminium chloride and anhydrous tetraethylammonium chloridewere, respectively, dissolved, each in an amount of 1.0 mole/liter, inmixed solvents of dehydrated propylene carbonate and dimethyl carbonateat different ratios, thereby obtaining a non-aqueous electrolyte. Moreparticularly, the mixing ratios of the propylene carbonate and dimethylcarbonate were changed. The resultant electrolytes were subjected tomeasurement of conductivity. The results are shown in FIG. 4. FIG. 4reveals that the conductivity increases with an increasing content ofthe dimethyl carbonate.

The non-aqueous electrolyte having a mixing ratio of propylene carbonateand dimethyl carbonate of 3:2 with which the conductivity becomes thehighest among those electrolytes shown in FIG. 4 was used to make a cellalong with the anode and cathode of Example 1. The cell was subjected tomeasurement of discharge characteristic at constant currents of 0.1 mAand 1.0 mA, respectively. With the constant current discharge at 0.1 mA,10000 minutes or more cycles of discharge were possible. When thedischarge was effected at a constant current of 1.0 mA, a good dischargecharacteristic as shown in FIG. 5 could be obtained.

Comparative Example 3

The general procedure of Example 2 was repeated without use of anhydroustetraethylammonium chloride, thereby obtaining a non-aqueous electrolyteand making a cell. The cell was subjected to measurement of a dischargecharacteristic. With a constant current discharge at 0.1 mA, dischargebecame impossible after several minutes. The results of the constantcurrent discharge at 1.0 mA are shown in FIG. 5.

These results reveal that the cell of Example 2 has a high utilizationefficiency than the cell of Comparative Example 3, with the loadcharacteristic being improved.

EXAMPLE 3

3.3 moles/liter of anhydrous aluminium chloride and 1.65 moles/liter ofanhydrous trimethylphenylammonium chloride were dissolved in dehydrated1,2-dichlorobenzene to obtain a non-aqueous electrolyte.

A cathode made of a platinum plate and an anode made of an Al plate wereimmersed in the non-aqueous electrolyte. A current with a quantity of0.4 mA.hr/cm² was passed to both plates at 25° C., whereupon a thin filmwith a metallic luster was formed on the platinum plate surface. Thethin film was subjected to analysis by means of an energy dispersedX-type analyzer (Delta Systems, Kebech Inc.), revealing that the filmconsisted of Al.

When the current was passed to the platinum and aluminium plates whilereversing the polarities, the thin film having a metallic luster on theplatinum plate was dissolved in the electrolyte. By this, it wasconfirmed that the electrodeposition and dissolution of Al could bereversibly realized.

EXAMPLE 4

The general procedure of Example 3 was repeated using 1,2-dichloroethaneas the non-aqueous solvent, thereby obtaining a non-aqueous electrolyteand electrodepositing aluminium. The resultant Al thin film had a smoothsurface and could be reversibly dissolved in the electrolyte.

EXAMPLE 5

The general procedure of Example 3 was repeated using acetonitrile asthe non-aqueous solvent, thereby obtaining a non-aqueous electrolyte andelectrodepositing aluminium. The resultant Al thin film had a smoothsurface.

EXAMPLE 6

The general procedure of Example 3 was repeated except that 1.5moles/liter of trimethylbenzylammonium chloride was used as thequaternary ammonium salt and that the concentration of aluminiumchloride was 3.0 mole/liter, thereby obtaining a non-aqueous electrolyteand electrodepositing aluminium. The resultant aluminium thin film had asmooth surface. The thin film could be reversibly dissolved in theelectrolyte.

EXAMPLE 7

The general procedure of Example 6 was repeated using 1,2-dichloroethaneas the non-aqueous solvent, thereby obtaining a non-aqueous electrolyteand electrodepositing aluminium. The resultant Al thin film had a smoothsurface and could be reversibly dissolved in the electrolyte.

EXAMPLE 8

The general procedure of Example 6 was repeated using acetonitrile asthe non-aqueous solvent, thereby obtaining a non-aqueous electrolyte andelectrodepositing aluminium therefrom. The resultant Al thin film had asmooth surface.

EXAMPLE 9

The general procedure of Example 3 was repeated except thattetraethylammonium chloride was used as the quaternary ammonium salt and1,2-dichloroethane was used as the non-aqueous solvent and that theconcentration of aluminium chloride was 2.0 moles/liter and theconcentration of the tetraethylammonium chloride was 1.0 mole/liter,thereby obtaining a non-aqueous electrolyte and electrodepositingaluminium. The resultant Al thin film had a smooth surface and could bereversibly dissolved in the electrolyte.

EXAMPLE 10

The general procedure of Example 9 was repeated usingl,2-dichlorobenzene as the non-aqueous solvent, thereby obtaining anon-aqueous electrolyte and electrodepositing aluminium therefrom. Theresultant Al thin film had a smooth surface and could be reversiblydissolved in the electrolyte.

EXAMPLE 11

The general procedure of Example 9 was repeated using acetonitrile asthe non-aqueous solvent, thereby obtaining a non-aqueous electrolyte andelectrodepositing aluminium therefrom. The resultant Al thin film had asmooth surface.

EXAMPLE 12

The general procedure of Example 3 was repeated usingtriethylmethylammonium chloride as the quaternary ammonium salt, therebyobtaining a non-aqueous electrolyte and electrodepositing aluminium.therefrom. The resultant Al thin film had a smooth surface and could bereversibly dissolved in the electrolyte.

EXAMPLE 13

The general procedure of Example 12 was repeated using1,2-dichloroethane as the non-aqueous solvent, thereby obtaining anon-aqueous electrolyte and electrodepositing aluminium therefrom. Theresultant Al thin film had a smooth surface and could be reversiblydissolved in the electrolyte.

EXAMPLE 14

The general procedure of Example 12 was repeated using acetonitrile asthe non-aqueous solvent, thereby obtaining a non-aqueous electrolyte andelectrodepositing aluminium therefrom. The resultant Al thin film had asmooth surface.

EXAMPLE 15

The general procedure of Example 3 was repeated except thattriethylphenylammonium chloride was used as the quaternary ammonium saltand 1,2-dichloroethane was used as the non-aqueous solvent and that theconcentration of aluminium chloride was 4.0 moles/liter and theconcentration of the triethylphenylammonium chloride was 2.5moles/liter, thereby obtaining a non-aqueous electrolyte andelectrodepositing aluminium. The resultant Al thin film had a smoothsurface and could be reversibly dissolved in the electrolyte.

EXAMPLE 16

The general procedure of Example 15 was repeated using1,2-dichloroethane as the non-aqueous solvent, thereby obtaining anon-aqueous electrolyte and electrodepositing aluminium therefrom. Theresultant Al thin film had a smooth surface and could be reversiblydissolved in the electrolyte.

EXAMPLE 17

The general procedure of Example 15 was repeated using acetonitrile asthe non-aqueous solvent, thereby obtaining a non-aqueous electrolyte andelectrodepositing aluminium therefrom. The resultant Al thin film had asmooth surface.

EXAMPLE 18

The general procedure of Example 3 was repeated usingtriethylbenzylammonium chloride as the quaternary ammonium salt, therebyobtaining a non-aqueous electrolyte and electrodepositing aluminiumtherefrom. The resultant Al thin film had a smooth surface and could bereversibly dissolved in the electrolyte.

EXAMPLE 19

The general procedure of Example 18 was repeated using1,2-dichloroethane as the non-aqueous solvent, thereby obtaining anon-aqueous electrolyte and electrodepositing aluminium therefrom. Theresultant Al thin film had a smooth surface and could be reversiblydissolved in the electrolyte.

EXAMPLE 20

The general procedure of Example 18 was repeated using acetonitrile asthe non-aqueous solvent, thereby obtaining a non-aqueous electrolyte andelectrodepositing aluminium therefrom. The resultant Al thin film had asmooth surface.

EXAMPLE 21

The general procedure of Example 3 was repeated usingtetramethylammonium chloride as the quaternary ammonium salt, therebyobtaining a non-aqueous electrolyte and electrodepositing aluminiumtherefrom. The resultant Al thin film had a smooth surface and could bereversibly dissolved in the electrolyte.

EXAMPLE 22

The general procedure of Example 21 was repeated using1,2-dichloroethane as the non-aqueous solvent, thereby obtaining anon-aqueous electrolyte and electrodepositing aluminium therefrom. Theresultant Al thin film had a smooth surface and could be reversiblydissolved in the electrolyte.

EXAMPLE 23

The general procedure of Example 21 was repeated using acetonitrile asthe non-aqueous solvent, thereby obtaining a non-aqueous electrolyte andelectrodepositing aluminium therefrom. The resultant Al thin film had asmooth surface.

EXAMPLE 24

The general procedure of Example 3 was repeated except that a copperplate was used as the cathode, thereby obtaining a non-aqueouselectrolyte, electrodepositing aluminium and reversibly dissolving thedeposited aluminium. Ten cycles of the electrodeposition and dissolutionof aluminium were repeated. As a result, the deposited aluminiumobtained after the ten cycles was free of any arborescent surface andhad a smooth surface. Accordingly, when a secondary cell was fabricatedusing the non-aqueous electrolyte of this example, short-circuitingbetween the cathode and the anode at the time of charge could beprevented.

EXAMPLE 25

The general procedure of Example 24 was repeated using1,2-dichloroethane as the non-aqueous solvent, thereby obtaining anon-aqueous electrolyte, electrodepositing aluminium therefrom andreversibly dissolving the aluminium. As a result, it was found that thesurface of the deposited aluminium after the ten cycles was notdendritic but smooth.

EXAMPLE 26

The general procedure of Example 24 was repeated except thattrimethylbenzylammonium chloride was used as the quaternary ammoniumsalt and that the concentration of aluminium chloride was 3.0moles/liter and the concentration of the trimethylbenzylammoniumchloride was 1.5 moles/liter, thereby obtaining a non-aqueouselectrolyte, electrodepositing aluminium and reversibly dissolving thedeposited aluminium. As a result, it was found that the surface of thedeposited aluminium after the ten cycles was not dendritic but smooth.

EXAMPLE 27

The general procedure of Example 26 was repeated using1,2-dichloroethane as the non-aqueous solvent, thereby obtaining anon-aqueous electrolyte, electrodepositing aluminium therefrom andreversibly dissolving the aluminium. As a result, it was found that thesurface of the deposited aluminium after the ten cycles was notdendritic but smooth.

EXAMPLE 28

The general procedure of Example 24 was repeated except thattetraethylammonium chloride was used as the quaternary ammonium salt andthat the concentration of aluminium chloride was 2.0 moles/liter and theconcentration of the tetraethylammonium chloride was 1.0 mole/liter,thereby obtaining a non-aqueous electrolyte, electrodepositing aluminiumand reversibly dissolving the deposited aluminium. As a result, it wasfound that the surface of the deposited aluminium after the ten cycleswas not dendritic but smooth.

EXAMPLE 29

The general procedure of Example 28 was repeated using1,2-dichloroethane as the non-aqueous solvent, thereby obtaining anon-aqueous electrolyte, electrodepositing aluminium therefrom andreversibly dissolving the aluminium. As a result, it was found that thesurface of the deposited aluminium after the ten cycles was notdendritic but smooth.

EXAMPLE 30

The general procedure of Example 24 was repeated usingtriethylmethylammonium chloride as the quaternary ammonium salt, therebyobtaining a non-aqueous electrolyte, electrodepositing aluminiumtherefrom and reversibly dissolving the aluminium. As a result, it wasfound that the surface of the deposited aluminium after the ten cycleswas not dendritic but smooth.

EXAMPLE 31

The general procedure of Example 30 was repeated using1,2-dichloroethane as the non-aqueous solvent, thereby obtaining anon-aqueous electrolyte, electrodepositing aluminium therefrom andreversibly dissolving the aluminium. As a result, it was found that thesurface of the deposited aluminium after the ten cycles was notdendritic but smooth.

EXAMPLE 32

The general procedure of Example 30 was repeated except thattriethylphenylammonium chloride was used as the quaternary ammonium saltand 1,2-dichloroethane was used as the non-aqueous solvent and that theconcentration of aluminium chloride was 4.0 moles/liter and theconcentration of the triethylphenylammonium chloride was 2.5moles/liter, thereby obtaining a non-aqueous electrolyte,electrodepositing aluminium and reversibly dissolving the depositedaluminium. As a result, it was found that the surface of the depositedaluminium after the ten cycles was not dendritic but smooth.

EXAMPLE 33

The general procedure of Example 32 was repeated using1,2-dichloroethane as the non-aqueous solvent, thereby obtaining anon-aqueous electrolyte, electrodepositing aluminium therefrom andreversibly dissolving the aluminium. As a result, it was found that thesurface of the deposited aluminium after the ten cycles was notdendritic but smooth.

EXAMPLE 34

The general procedure of Example 24 was repeated usingtriethylbenzylammonium chloride as the quaternary ammonium salt, therebyobtaining a non-aqueous electrolyte, electrodepositing aluminiumtherefrom and reversibly dissolving the aluminium. As a result, it wasfound that the surface of the deposited aluminium after the ten cycleswas not dendritic but smooth.

EXAMPLE 35

The general procedure of Example 34 was repeated using1,2-dichloroethane as the non-aqueous solvent, thereby obtaining anon-aqueous electrolyte, electrodepositing aluminium therefrom andreversibly dissolving the aluminium. As a result, it was found that thesurface of the deposited aluminium after the ten cycles was notdendritic but smooth.

As will be apparent from the foregoing, the non-aqueous electrolyte ofthe invention is applied to a cell which has an Al or Al alloy anode,the polarity at the time of discharge of the cell can be reduced withgood discharge characteristics. Moreover, aluminium can beelectrodeposited in this non-aqueous electrolyte. The reversible cycleof the electrodeposition and dissolution of aluminium is possible, sothat it will be possible to make a secondary cell which has good chargeand discharge characteristics and a high energy density.

What is claimed is:
 1. A non-aqueous electrolyte comprising, an aluminum halide and a quaternary ammonium halide in a non aqueous solvent, where the non aqueous solvent is an organic compound comprising a donor number of not larger than 5, and a molar ratio of the quaternary ammonium halide to the aluminum halide is in the range of 0.5:1 to 1:1.
 2. The non aqueous electrolyte of claim 1, wherein the organic compound is a member selected from the group consisting of 1,2-dichloroethane, 1,2-dichlorobenzene, 1,3-dichlorobenzene, and mixtures thereof.
 3. The non aqueous electrolyte of claim 1, wherein a concentration of the aluminum halide in the non aqueous electrolyte is in the range of from 0.1 to 2.0 moles/liter of the electrolyte.
 4. The non aqueous electrolyte of claim 1, wherein the aluminum halide is of the formula AlX, wherein X represents Cl, Br, or I.
 5. The non aqueous electrolyte of claim 1, wherein the aluminum halide is present in an amount of 0.1 to 10.0 moles/liter of the electrolyte.
 6. The non aqueous electrolyte of claim 1, wherein the quaternary ammonium halide is of the formula:

wherein R1, R2, R3, and R4 independently represent a hydrocarbon group and Y— is a counter ion selected from the group consisting of Cl—, Br—, or I—.
 7. The non aqueous electrolyte of claim 6, wherein the hydrocarbon group has up to 10 carbon atoms.
 8. A non-aqueous electrolyte comprising, an aluminum halide and a quaternary ammonium halide in a non aqueous solvent, where the non aqueous solvent is an organic compound comprising a donor number of not larger than 5, and a molar ratio of the quaternary ammonium halide to the aluminum halide being not larger than 1:1; and wherein the organic compound is a member selected from the group consisting of 1,2-dichloroethane, 1,2-dichlorobenzene, 1,3-dichlorobenzene, and mixtures thereof.
 9. The non aqueous electrolyte of claim 8, wherein a concentration of the aluminum halide in the non aqueous electrolyte is in the range of from 0.1 to 2.0 moles/liter of the electrolyte.
 10. The non aqueous electrolyte of claim 8, wherein the aluminum halide is of the formula AlX, wherein X represents Cl, Br, or I.
 11. The non aqueous electrolyte of claim 8, wherein the aluminum halide is present in an amount of 0.1 to 10.0 moles/liter of the electrolyte.
 12. The non aqueous electrolyte of claim 8, wherein the quaternary ammonium halide is of the formula:

wherein R1, R2, R3, and R4 independently represent a hydrocarbon group and Y— is a counter ion selected from the group consisting of Cl—, Br—, or I—.
 13. The non aqueous electrolyte of claim 12, wherein the hydrocarbon group has up to 10 carbon atoms.
 14. A non-aqueous electrolyte comprising, an aluminum halide and a quaternary ammonium halide in a non aqueous solvent, where the non aqueous solvent is an organic compound comprising a donor number of not larger than 5, and a molar ratio of the quaternary ammonium halide to the aluminum halide is in the range of 0.5:1 to 1:1, and wherein the organic compound is a member selected from the group consisting of 1,2-dichloroethane, 1,2-dichlorobenzene, 1,3-dichlorobenzene, and mixtures thereof.
 15. The non aqueous electrolyte of claim 14, wherein the aluminum halide is of the formula AlX, wherein X represents Cl, Br, or I.
 16. The non aqueous electrolyte of claim 14, wherein the aluminum halide is present in an amount of 0.1 to 10.0 moles/liter of the electrolyte.
 17. The non aqueous electrolyte of claim 14, wherein the quaternary ammonium halide is of the formula:

wherein R1, R2, R3, and R4 independently represent a hydrocarbon group and Y— is a counter ion selected from the group consisting of Cl—, Br—, or I—.
 18. The non aqueous electrolyte of claim 17, wherein the hydrocarbon group has up to 10 carbon atoms. 